Suppression of P50 evoked potential component, schizotypal beliefs and smoking

Suppression of the P50 component of the evoked potential is an electrophysiological index of sensory gating that is blunted in schizophrenia spectrum disorders. Although P50 suppression is thought to be related to symptomatology, this is yet to be shown. The failure to demonstrate this relation has led some to argue that P50 suppression and symptomatology are not related. However, a possible confound has recently been corroborated [i.e., chronic smoking is related to superior P50 suppression [Crawford et al., Neuroscience Letters 317 (2002) 151]], and a relation has been found in questionnaire-defined individuals with indications of schizotypy [i.e., psychometric schizotypy is related to poor P50 suppression [Croft et al., Biological Psychiatry 50 (2001) 441]]. The present study attempted to replicate and extend both studies by examining P50 suppression, smoking histories, psychometric schizotypy and NEO Five-Factor Inventory (NEO-V) scores in 37 healthy participants. Replicating Crawford et al., P50 suppression was better in the heavier smokers. Providing a partial replication of Croft et al., P50 suppression was inversely related to schizotypy scores in participants who smoked little or not at all; however, P50 suppression was positively related to schizotypy in heavier smokers. Covarying for age and NEO-V scale scores had little effect on these relations. The findings provide evidence of important confounds that would limit our ability to detect P50 suppression/symptom relations in schizophrenia.